The Role of Windows Communication Foundation

As standardization of Web services security, policy, and addressing became more important, Microsoft provided its own implementation of the WS-Security, WS-Policy, and WSAddressing specifications in its Web Services Enhancements (WSE) package, available as a free download from the Microsoft Web site. What does all this mean if you are developing Web services using Visual Studio 2008? Well, with Visual Studio 2008, you can build Web services by using two technologies—ASP.NET and WCF. Ordinary ASP.NET Web services do not directly support the various WS-* specifications. Instead, you can use Microsoft’s WSE package to provide features such as security.

So, by using Visual Studio, the .NET Framework, and WSE, you can quickly build Web services and client applications that can communicate and interoperate with Web services and client applications running on any operating system. Why then do you need WCF? Well, first, WCF is a more recent technology that emerged as part of version 3.0 of the .NET Framework. It provides its own fully integrated implementation of the common WS-* specifications without requiring you to download, install, and configure additional packages. Second, Web services are just one technology that you can use to create distributed applications for the Windows operating systems. Others include Enterprise Services, .NET Framework Remoting, and Microsoft Message Queue (MSMQ). If you are building a distributed application for Windows, which technology should you use, and how difficult will it be to switch later if you need to? The purpose of WCF is to provide a unified programming model for many of these technologies so that you can build applications that are as independent as possible from the underlying mechanism being used to connect services and applications. (Note that WCF applies as much to services operating in non-Web environments as it does to the World Wide Web.) It is actually very difficult, if not impossible, to completely divorce the programmatic structure of an application or service from its communications infrastructure, but WCF lets you come very close to achieving this aim much of the time. Additionally, by using WCF, you can maintain backward compatibility with many of the earlier technologies. For example, a WCF client application can easily communicate with a Web service that you created by using WSE.

To summarize, if you are considering building distributed applications and services for Windows, you should use WCF. The exercises in this chapter will show you how.

Building a Web Service

In this section, you will create the ProductsService Web service. This Web service exposes two Web methods. The first method enables the user to calculate the cost of buying a specified quantity of a particular product in the Northwind database, and the second method takes the name of a product and returns all the details for that product.

628 Part VI Building Web Applications

Creating the ProductsService Web Service

In the first exercise, you will create the ProductsService Web service and examine the

example code generated by Visual Studio 2008 whenever you create a new WCF service project. In subsequent exercises, you will define and implement the HowMuchWillItCost Web

method and then test the Web method to ensure that it works as expected.

Create the Web service, and examine the example code

1.Start Visual Studio 2008 if it is not already running.

2.If you are using Visual Studio 2008 Professional Edition or Enterprise Edition, on the File menu, point to New, and then click Web Site.

3.If you are using Microsoft Visual Web Developer 2008 Express Edition, on the File menu, click New Web Site.

4.In the New Web Site dialog box, click the WCF Service template. Select File System in the Location drop-down list box, and specify the \Microsoft Press\Visual CSharp Step

By Step\Chapter 30\NorthwindServices folder under your Documents folder. Set the

Language to Visual C#, and then click OK.

Visual Studio 2008 generates a Web site containing folders called App_Code and

App_Data, a file called Service.svc, and a configuration file called Web.config. The code for an example Web service is defined in the Service class, stored in the file Service.cs in the App_Code folder, and displayed in the Code and Text Editor window. The Service class implements an example interface called IService, stored in the file IService.cs in the App_Code folder.

5.Click the C:\...\NorthwindServices\ project. In the Properties window, set the Use dynamic ports property to False, and set the Port number property to 4500.

By default, the Development Web server provided with Visual Studio 2008 picks a port at random to reduce the chances of clashing with any other ports used by other network services running on your computer. This feature is useful if you are building and testing ASP.NET Web sites in a development environment prior to copying them to a production server such as Microsoft Internet Information Services (IIS). However, when building a Web service, it is more useful to use a fixed port number because client applications need to be able to connect to it.

6.Expand the App_Code folder, right-click the Service.cs file, and then click Rename. Change the name of the file to ProductsService.cs.

7.Using the same technique, change the name of the IService.cs file to IProductsService.cs.

8.Double-click the IProductsService.cs file to display it in the Code and Text Editor window.

This file contains the definition of an interface called IService. At the top of the IProductsService.cs file, you will find using statements referencing the System, System. Collections.Generic, and System.Text namespaces (which you have met before), followed by two additional statements referencing the System.ServiceModel and System.Runtime. Serialization namespaces.

The System.ServiceModel namespace contains the classes used by WCF for defining services and their operations. WCF uses the classes in the System.Runtime.Serialization

namespace to convert objects to a stream of data for transmission over the network (a process known as serialization) and to convert a stream of data received from the

network back to objects (deserialization). You will learn a little about how WCF serializes and deserializes objects later in this chapter.

The primary contents of the IProductsService file are an interface called IService and a class called CompositeType. The IService interface is prefixed with the ServiceContract attribute, and the CompositeType class is tagged with the DataContract attribute.

Because of the structure of a WCF service, you can adopt a “contract-first” approach to

development. When performing contract-first development, you define the interfaces, or contracts, that the service will implement, and then you build a service that conforms

to these contracts. This is not a new technique, and you have seen examples of this strategy throughout this book. The point behind using contract-first development is that you can concentrate on the design of your service. If necessary, it can quickly be reviewed to ensure that your design does not introduce any dependencies on specific hardware or software before you perform too much development; remember that in many cases client applications might not be built using WCF and might not even be running on Windows.

The ServiceContract attribute marks an interface as defining methods that the class

implementing the Web service will expose as Web methods. The methods themselves are tagged with the OperationContract attribute. The tools provided with Visual Studio

2008 use these attributes to help generate the appropriate WSDL document for the service. Any methods in the interface not marked with the OperationContract attribute

will not be included in the WSDL document and therefore will not be accessible to client applications using the Web service.

If a Web method takes parameters or returns a value, the data for these parameters and value must be converted to a format that can be transmitted over the network and then converted back again to objects—this is the process known as serialization and deserialization mentioned earlier. The various Web services standards define mechanisms for specifying the serialized format of simple data types, such as numbers and strings, as part of the WSDL description for a Web service. However, you can also define your own complex data types based on classes and structures. If you make use of these

types in a Web service, you must provide information on how to serialize and deserialize them. If you look at the definition of the GetDataUsingDataContract method in the

Define the contracts for the ProductsService Web service

1.Display the IProductsService.cs file in the Code and Text Editor window. Change the name of the IService interface to IProductsService, as shown here in bold type:

[ServiceContract]

public interface IProductsService

{

...

}

2.In the IProductsService interface, remove the definitions of the GetData and

GetDataUsingDataContract methods, and replace them with the HowMuchWillItCost and GetProductInfo methods, shown in the following code. Make sure you retain the OperationContract attribute for each Web method.

[ServiceContract]

public interface IProductsService

{

[OperationContract]

decimal HowMuchWillItCost(int productID, int howMany);

[OperationContract]

ProductInfo GetProductInfo(int productID);

}

The HowMuchWillItCost method takes a product ID and a quantity and returns a decimal value specifying the amount this quantity will cost.

The GetProductInfo method takes a product ID and returns a ProductInfo object containing the details of the specified product. You will define the ProductInfo class in

the next step.

3.Remove the CompositeType class from the IProductsService.cs file, and add the ProductInfo class, including the DataContract attribute, like this:

[DataContract]

public class ProductInfo

{

}

4.Add the following public properties to the ProductInfo class. There is one property for each of the columns in the Products table in the database. Mark each property with the

DataMember attribute:

[DataContract]

public class ProductInfo

{

[DataMember]

public int ProductID {get; set;}

[DataMember]

public string ProductName {get; set;}

[DataMember]

public int? SupplierID {get; set;}

[DataMember]

public int? CategoryID {get; set;}

[DataMember]

public string QuantityPerUnit {get; set;}

[DataMember]

public decimal? UnitPrice {get; set;}

[DataMember]

public short? UnitsInStock {get; set;}

[DataMember]

public short? UnitsOnOrder {get; set;}

[DataMember]

public short? ReorderLevel {get; set;}

[DataMember]

public bool? Discontinued {get; set;}

}

Notice that the properties that correspond to columns that allow null values in the database are defined by using nullable types (apart from QuantityPerUnit, which is a reference type that allows null values automatically because it is a string). Also, you

should ensure that all properties support read and write access. The serialization mechanism used by WCF is automatic and largely transparent as long as you follow a few simple rules when defining the class. In particular, serialization can be used only when the runtime transmits objects that contain public fields and properties; private members will not be serialized. Also note that all properties must have both get and set accessors. This is because the XML serialization process must be able to write this data back to the object after it has been transferred. Additionally, the class must provide a default (with no parameters) constructor.

It is common to design classes used for SOAP purely as containers for transmitting data. If necessary, you can define additional functional classes that act as façades, providing the business logic for these data structures. Users and applications can gain access to the data by using these business façades.

Note You can customize the serialization mechanism using the various SOAP attribute classes of the System.Xml.Serialization namespace or define your own XML serialization mechanism by implementing the ISerializable interface of the System.Runtime.Serialization

namespace.

The next stage is to define the ProductsService class that implements the IProductsService interface. The methods in this class will retrieve product information from the Northwind database, so you will start by adding an entity class and data context for retrieving this information.

Implement the IProductsService interface

1.On the Website menu, click Add New Item.

2.In the Add New Item dialog box, click the LINQ to SQL Classes template, type Product. dbml in the Name text box, select Visual C# in the Language drop-down list, and then click Add.

3.If you are using Visual Studio 2008 Professional Edition or Enterprise Edition, on the

View menu, click Server Explorer.

4.If you are using Visual Web Developer 2008 Express Edition, on the View menu, click

Database Explorer.

5.In Server Explorer (if you are using Visual Studio 2008) or Database Explorer (if you are

using Visual Web Developer 2008 Express Edition), expand the data connection for the Northwind database (YourComputer\sqlexpress.Northwind.dbo or Northwind.mdf), and then expand Tables.

6.Click the Products table, and drag it onto the Object Relational Designer window.

7.On the File menu, click Save All.

8.Display the ProductsService.cs file in the Code and Text Editor window. Remove the Service class from this file.

9.Add the ProductsService class to the file, and specify that it should implement the IProductsService interface, as shown here:

public class ProductsService : IProductsService

{

}

10. Add the HowMuchWillItCost method to the Service class, as follows:

public class ProductsService : IProductsService

{

public decimal HowMuchWillItCost(int productID, int howMany)

{

ProductDataContext pdc = new ProductDataContext(); decimal? cost = pdc.Products.Single(

p => p.ProductID == productID).UnitPrice;

decimal totalCost = 0; if (cost.HasValue)

Before you can use the Web service, you must update the configuration in the Service.svc file to refer to the ProductsService class in the ProductsService.cs file. You must also modify the

Web.config file to reflect the new name of the Web service.

Configure the Web service

1.In Solution Explorer, double-click the Service.svc file to display it in the Code and Text Editor window. Update the Service and CodeBehind attributes of the ServiceHost directive, as shown here in bold type:

<%@ ServiceHost Language=”C#” Debug=”true” Service=”ProductsService” CodeBehind=”~/App_Code/ProductsService.cs” %>

Note The Error List window for the Service.svc file might display the same errors as before. Again, these errors should disappear when you rebuild the application, so you can safely ignore them.

2.In Solution Explorer, double-click the Web.config file. In the Code and Text Editor window, locate the <system.serviceModel> element. This element contains the following <services> element, specifying the endpoint binding information for the Web

service implemented by this solution. (You can ignore the service that implements the IMetadataExchange contract in this chapter.)

<system.serviceModel>

<services>

<service name=”Service” behaviorConfiguration=”ServiceBehavior”> <!-- Service Endpoints -->

<endpoint address=”” binding=”wsHttpBinding” contract=”IService”/>

...

</service>

</services>

<behaviors>

...

</behaviors>

</system.serviceModel>

WCF uses the notion of endpoints to associate a network address with a specific Web

service. If you are hosting a Web service by using IIS or the ASP.NET Development Server, you should leave the address property of your endpoint blank because IIS listens

for incoming requests on an address specified by its own configuration information.

Note You can build your own custom host applications if you don’t want to use IIS or the ASP.NET Development Server. In these situations, you must specify an address for the ser-

vice as part of the endpoint definition. For more information about endpoints and custom hosts, see Microsoft Windows Communication Foundation Step by Step.

3.In the Web.config file, change the name attribute of the Service element and the contract attribute of the endpoint element to refer to the ProductsService service and the IProductsService contract, as shown here in bold type:

<system.serviceModel>

<services>

<service name=”ProductsService” behaviorConfiguration=”ServiceBehavior”> <!-- Service Endpoints -->

<endpoint address=”” binding=”wsHttpBinding” contract=”IProductsService”/>

...

</service>

</services>

<behaviors>

...

</behaviors>

</system.serviceModel>

4.On the File menu, click Save All.

5.In Solution Explorer, right-click Service.svc, and then click View in Browser.

Internet Explorer starts and displays the following page, confirming that you have successfully created and deployed the Web service and providing helpful information describing how to create a simple client application that can access the Web service.

Note If you click the link shown on the Web page (http://localhost:4500/ NorthwindServices/Service.svc?wsdl), Internet Explorer displays a page containing the

WSDL description of the Web service. This is a long and complicated piece of XML, but Visual Studio 2008 can take the information in this description and use it to generate a class that a client application can use to communicate with the Web service.

6. Close Internet Explorer, and return to Visual Studio 2008.